I have an Ampeg R100 and love it. But it does have an extension speaker jack. Since it only has one 15", this would be helpful. I have an old Kustom 50 with one 15 in it. it hums like hell and rather than try to get it fixed, i'd like to just use it as an extension cab. How do i do this with the ampeg. This would be in addition to the speaker in the ampeg, not instead of it. Thanks!